土壤中细菌总数的测定

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1、实验三土壤中细菌总数的测定一教学要求通过土壤中细菌总数的测定，了解微生物数量的测定方法，掌握平板菌落计数的原理和方法二实验原理1、测定微生物生长的方法DirectmethodsDirectcounting，CoultercounterIndirectmethodsViableCellmethods，Membranefiltration，turbiditymethods，mostprobablenumber(MPN),DetectchemicalproductsormetabolicactivityAlternativemethodsforv

2、iablecellcounts2、Theplatecount(viablecount)Thenumberofbacteriainagivensampleisusuallytoogreattobecounteddirectly.However,ifthesampleisseriallydilutedandthenplatedoutonanagarsurfaceinsuchamannerthatsingleisolatedbacteriaformvisibleisolatedcolonies,thenumberofcoloniescanbeus

3、edasameasureofthenumberofviable(living)cellsinthatknowndilution.Colony-FormingUnits(CFUs)However,keepinmindthatiftheorganismnormallyformsmultiplecellarrangements,suchaschains,thecolony-formingunitmayconsistofachainofbacteriaratherthanasinglebacterium.Inaddition,someoftheba

4、cteriamaybeclumpedtogether.Therefore,whendoingtheplatecounttechnique,wegenerallysaywearedeterminingthenumberofColony-FormingUnits(CFUs)inthatknowndilution.Byextrapolation,thisnumbercaninturnbeusedtocalculatethenumberofCFUsintheoriginalsample.calculatethenumberofCFUsintheor

5、iginalsamplenumberofCFUspermlofsample=numberofcolonies(30-300plate)XthedilutionfactoroftheplatecountedForamoreaccuratecountitisadvisabletoplateeachdilutioninduplicateortriplicateandthenfindanaveragecount.三材料与器材无菌培养皿12套、1mL无菌移液管10支、土壤样品、天平等。四操作步骤无菌平皿编号→制备土壤稀释液→倾注平板→培养(48h)→

6、计数五注意事项倒平板时要注意控制培养基的温度。稀释操作时，要尽量减少样品稀释误差，而且每个稀释度的菌液应各用一支无菌吸管。为使菌落能在平板上均匀分布，样品液加入平皿后，应尽快倾注培养基并旋转混匀。六思考题要测定某种液体饮料中的活细菌总数，除了采用平板菌落计数法外，还可采用哪些方法？